Field of the Invention
The invention lies in the internal combustion technology field. More specifically, the invention relates to a method for controlling an internal combustion engine wherein a possible change in the fuel quality between the shutting down and subsequent restarting of the internal combustion engine is taken into account.
Fuels for internal combustion engines are composed of a mixture of hydrocarbon compounds which can contain additives of oxygen-containing, organic components, and additives for improving the properties.
Depending on the proportion of the different hydrocarbons in the fuel, there are different effects on the operating behavior of the internal combustion engine, in particular the power, the consumption, the acoustics, the starting capability, and the exhaust gas emissions are influenced. Modern internal combustion engines must be capable of processing fuels of differing quality without appreciable adverse effects on the operating behavior.
At present, changes in the fuel quality are detected using what is referred to as a fuel quality detector or the unsmooth running method and compensated by changing the injection time period. In those method, which are already applied, the rise in the rotational speed is evaluated when the internal combustion engine starts, or the fluctuations in the rotational speed are evaluated during starting. If the rise in the rotational speed or the fluctuations in the rotational speed do not lie within a permitted, predefined confidence limit, the injection time period is correspondingly corrected. The specific value of the correction is however calculated relatively imprecisely so that under certain circumstances the correction may be excessive. In particular, given what is referred to as a xe2x80x9cpoor start,xe2x80x9d, the injection time period is changed in such a way that the fuel/air mixture becomes richer, for which reason the fuel/air mixture after a refueling process of a very good fuel can become too rich. The internal combustion engine then starts only poorly or even does not start at all any more. Furthermore, there is the risk that the undesired rotational-speed behavior was not caused by a changed quality in the fuel but rather has other fault sources.
U.S. Pat. No. 5,197,445 (corresponding to German patent application DE 40 27 947 A1) describes various methods with which the changes in fuel quality can be taken into account. On the one hand, after each time the vehicle driven by the internal combustion engine is refueled the control error in the lambda control circuit can be measured and an adaptation value can be changed in such a way that the control error which is determined disappears. This method has the disadvantage that it functions only if the lambda control is active, which is, however, not the case in particular when the internal combustion engine is cold. On the other hand, methods are proposed which, even when the internal combustion engine is cold, ensure that the internal combustion engine is operationally capable if the fuel composition changes severely when refueling occurs, for example as a result of the fact that a tank containing fuel has almost been run empty and that a fuel which predominantly contains methanol has been used for refueling. Using the tank levels before and after the refueling and on the basis of the data on commercially available fuels, an estimate of what fuel compositions may be present is made. The pilot control values are then changed for the operation of the internal combustion engine with fuels of the possible compositions, and an examination is made, assuming the composition with which the internal combustion engine runs best. The internal combustion engine is then regulated further using these values.
It is accordingly an object of the invention to provide a method of controlling an internal combustion engine, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which enables fault-free running of the internal combustion engine to be achieved even if refueling has been carried out with fuel that differs greatly in its composition from the fuel which was fed to the internal combustion engine before the refueling.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling an internal combustion engine, which comprises:
determining a basic injection time period in dependence on operating parameters of the internal combustion engine;
correcting the basic injection time period with a correction factor taking into account a possible change in a quality of fuel fed to the internal combustion engine between a shutting down and a restarting of the internal combustion engine;
weighting the correction factor with a weighting factor; and
selecting the weighting factor in dependence on a filling level of a fuel reservoir container holding the fuel when the internal combustion engine is shut down, and on the filling level when the internal combustion engine is restarted.
In accordance with an added feature of the invention, the method comprises:
determining and storing a first value for the filling level when the internal combustion engine is shut down;
determining a second value for the filling level when the internal combustion engine is subsequently restarted;
determining a percentage that constitutes a measure for a possible change in the fuel quality between the engine shutdown and the engine restart from the first and second values;
inputting the percentage as an input variable to a characteristic diagram; and
reading out values for the weighting factor from the characteristic diagram.
In accordance with an additional feature of the invention, the above-mentioned percentage is determined in accordance with the relationship:
qf1=(F2xe2x88x92F1)/F2xe2x88x92100%, 
where qf1 is the percentage, F1 is the first value of the filling level at shut-down of the internal combustion engine, and F2 is the second value of the filling level at the subsequent restart of the internal combustion engine.
In accordance with another feature of the invention, the relationship between the percentage and the weighting factor is determined experimentally.
In accordance with a further feature of the invention, the correction factor is weighted according to the relationship:
FAC_FQ_ADn+1=FAC_FQ_ADn 
wherein FAC_FQ_ADn+1 is a current correction factor, FAC_FQ_ADn is a previous correction factor for a detection of the fuel quality, and qf2 is the weighting factor.
In accordance with again a further feature of the invention, the weighting factor lies in a range from 0 to 0.999.
In accordance with a concomitant feature of the invention, the percentage is used in fault diagnostics of the internal combustion engine.
In other words, in the invention, an estimate of a possible change in fuel quality is carried out using a filling level change of the fuel reservoir container between the shutting down of the internal combustion engine and restarting of the internal combustion engine. If there is a specific quantity of fuel in the fuel reservoir container and the time when the internal combustion engine is shut down and if the quantity which is determined when the internal combustion engine is restarted is greater than said specific quantity, it can be assumed that the vehicle has been refueled. A percentage, which constitutes a measure of a possible change in the fuel quality, is determined as a function of the filling level before the shutting down and the filling level before the restarting.
Using this-information, it is possible to weight the change in the injection time period in addition to the detection of the fuel quality or unsmooth running method. The influence of the correction factor is reduced by a value which is dependent on the percentage change in the filling level.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method for controlling an internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.